A Practical Road to Lightweight Cars

Given the state of manufacturing art, the automobile industry has been taking an incremental approach to the use of new materials, gradually adopting new applications of aluminum, polymers, and advanced steels. For example, Ford is working closely with several aluminum companies on a project called Concept 2000 to produce 20 to 40 all-aluminum Taurus sedans, which the company is now testing and evaluating. The vehicle, which uses a unibody design, is only a few hundred pounds lighter than its steel counterpart, largely because the project engineers did not change the powertrain or suspension or redesign the vehicle to achieve other secondary weight savings. The project was intended only as a test of the manufacturability of an all-aluminum car, with the goal of identifying the changes in forming technology that would be needed to produce it. It is not yet clear whether Ford regards the experiment as successful.

Alcoa and Audi have collaborated on the Audi A8, a luxury sedan based on an aluminum space frame that is being produced at low volumes and marketed in Europe. Much of the weight savings gained by the use of aluminum are canceled out by accoutrements intended to boost the car’s appeal in a high-end market. The vehicle does, however, demonstrate the viability of a design that utilizes aluminum extrusions and castings as well as the wrought sheet used in the panels.

The automobile industry is also attempting to develop production techniques to put plastics on mass-produced vehicles (notably GM’s Saturn car lines), but even here the plastic components are not critical structural elements of the vehicle. All Saturns, for instance, use plastic body panels to cover a steel space frame. Because they have no structural role, the panels are made not of reinforced composites but of ordinary plastics, which can be produced in quantities of hundreds of thousands. The choice of material is governed less by weight considerations than by cosmetics: plastic panels give the vehicle its distinctive shape and resist dents and scratches. In fact, the weight saving achieved by the use of plastic panels is at least partly offset by the need to use more steel in structural components to maintain the expected level of performance.

Automakers have found that, with an aggressive effort, they can substitute polymers for steel in a handful of major nontraditional applications, such as roofs, hoods, floor pans, and engine cradles, but many are also discovering that the costs are too high and the weight savings unimpressive. GM has also experimented with glass fiber composites on the body panels of its APV vans for a number of years but recently concluded that the material is just too expensive. The company plans to return to using steel.

While they continue to experiment with glass fiber-reinforced polymers in niche-market vehicles-a well-established platform for innovation-automakers appear to have decided that these materials are not useful in applications with production volumes over 80,000, because at these volumes the benefits do not justify the costs. Moreover, it appears that the industry is already using plastics in most of the applications that are best suited to the material’s strengths. Further substitutions of plastics for steel will be much harder to accomplish, because these are the uses that capitalize specifically on the properties of metals.

Another material that may play a role in incremental change is high-strength steel. The thickness of steel parts used in automobiles is usually determined by the degree of stiffness they require, but in about 20 percent of applications the important property is strength. For instance, a beam in every car door protects passengers in the event of a crash. New high-strength steel alloys are two to three times as strong as conventional carbon steel, so a beam made of the new material could weigh one-half to one-third as much as the beam used in car doors today. A number of steel companies based in different countries have hired Porsche Engineering Services to come up with a body design incorporating all the potential applications of lightweight steel. They estimate that the body could weigh 10 to 20 percent less than a conventional steel unibody, at a cost up to 15 percent higher.

The Program for a New Generation of Vehicles, meanwhile, is investigating the potential uses of advanced steels, plastics, and aluminum, as well as such exotic-and expensive-substances as magnesium and titanium. At this early stage, researchers are trying to identify the technologies that could make up the platform for an affordable advanced vehicle. They appear to be focusing their efforts on the concept of a hybrid diesel-electric engine, for instance, and on aluminum as the dominant material for structural applications (although the vehicle will undoubtedly incorporate a variety of advanced materials for other uses.) Whether or not the program ultimately succeeds in developing a vehicle that is affordable-and there are rumblings that insiders believe it won’t-the effort will give the auto industry valuable experience with new materials and technologies.

Concentrating on What We Can Do

Whatever strategy the industry adopts, a vehicle made of lightweight materials is clearly going to cost more than today’s conventional car. The fuel economy of these vehicles is also going to depend upon a lot more than the shift to lightweight materials; significant gains will require changes in consumers’ expectations. Given our assumptions about how roomy a car should be, how swiftly it should accelerate, how fast it should go, and how comfortable it should be to ride in, it is difficult to make a car much lighter than, say, the all-aluminum Taurus that will still be a vehicle most of today’s consumers want to buy.

Nevertheless, the specter of the supercar haunts the debate over carbon-dioxide-induced global warming and feeds public pressure for government to mandate more radical reforms. If we can make a better tennis racket out of Kevlar, the argument goes, why can’t we make a better automobile out of the same kind of material? One answer is: although consumers may be willing to pay three times as much for their advanced composite tennis rackets, they are unlikely to be willing (or able) to pay quite the same price premium for an advanced composite car.

A supercar like that envisioned by the Program for a New Generation of Vehicles-one that achieves 80 miles per gallon, maintains the same level of convenience, and costs the same as today’s car-is beyond our capabilities today and for the near future. Any two of these three objectives can be achieved today, but putting all three together will require major technological breakthroughs. It is thus impractical for the industry to jettison today’s automobile designs and technology to pursue this technological chimera.

Because we cannot mass-produce an affordable, ultra-lightweight polymer-based vehicle body, we should concentrate instead on what we can do. For instance, we can make an aluminum body that performs as well as the steel alternative but costs only marginally more. The incremental application of the broad spectrum of advanced materials technologies available today can yield real benefits in efficiency, utility, and performance without incurring insupportable costs. Although relatively unexciting and unglamorous, incremental strategies for vehicle weight reduction are the only credible approach for beginning the transition to an economical, fuel-efficient vehicle.